The invention relates to a protective shield for a trimmer, whose cutting head, that is rotatable about an axis of rotation, supports a cutting thread that rotates in a rotational direction when the cutting head is rotated and then becomes aligned radially to the axis of rotation and determines a cutting circle that is at least partially covered by the protective shield. In the circumferential area of the cutting circle a cutting-to-length blade for the cutting thread is arranged on the protective shield.
Motor-driven brushcutters or trimmers of known configuration have a drive motor that is, for example, in the form of an internal combustion engine that drives a cutting head rotatable about an axis of rotation by means of a shaft supported in a guide tube. The cutting head supports a cutting thread that rotates in a rotational direction upon rotation of the cutting head and aligns itself approximately radially to the axis of rotation because of the occurring centrifugal forces. The rotational movement of the cutting thread determines a cutting circle. In the area of the cutting head, a protective shield is provided that covers the cutting circle of the cutting thread at least partially.
For mowing different plants such as grass or the like, the trimmer is aligned in the usual working position such that the cutting circle is positioned approximately parallel to the surface to be worked on. In the plane of the cutting circle, the rotating cutting thread cuts off the plants.
The cutting thread that is manufactured of flexible plastic material is subject to wear which primarily results in the cutting thread becoming shorter. From time to time, a manual or automatic adjustment of the cutting thread is required. For this purpose, the cutting thread is then moved out of a magazine provided on the cutting head in order to compensate the loss of length caused by wear. The length compensation is usually carried out so as to lead to an excess thread length. In order to prevent that a cutting circle that has too great a radius is generated, a cutting-to-length blade for cutting to length the cutting thread is arranged in the circumferential area of the cutting circle on the protective shield. During the first rotational movements following the length adjustment, the free end of the cutting thread having excess length impacts on the cutting edge of the cutting-to-length blade and is automatically cut to the predetermined length that should not be surpassed.
U.S. Pat. No. 5,531,403 discloses a trimmer having a protective shield with an integrated cutting-to-length blade. The cutting-to-length blade is arranged circumferentially relative to the cutting circle. Its cutting edge extends perpendicularly to the cutting circle and thus parallel to the axis of rotation of the cutting head. After automatic cutting to length of the cutting thread by means of the aforementioned cutting-to-length blade, the cutting thread has a free outer end that upon further trimmer operation is guided cyclically at high speed past the cutting edge of the cutting-to-length blade. In this area, an undesirably high noise development is observed.